It is in fact useful to be able not only to detect but also to quantify the phenomenon of hydroplaning occurring under a tire.
Hydroplaning is characterized by the momentary presence of an amount of water between a surface of the ground making up the road and a surface of the tread in contact with the ground. Now, the presence of water, even if momentary, between these two surfaces introduces the effect of an isolating film. Such a film prevents some or all force from being transferred between the tire or tires of the vehicle and the ground of the road. Consequently, this phenomenon of hydroplaning results in loss of grip, loss of traction when accelerating or braking, and also loss of steering control, in particular in road bends.
A film of water forms when the flow rate of water flowing between the two surfaces becomes greater than the flow rate of water that both the features of the road pavement and patterns in the tread of the tire can remove. This saturation effect therefore, for a constant height of water on the ground, increases more suddenly and more substantially with an increasing speed of the vehicle. Complementarily, at constant speed, the saturation effect occurs more rapidly if the height of water present on the surface of the ground increases.
The consequences of hydroplaning as a result of a saturation effect, especially during an acceleration by application of a driving force, during a deceleration by application of a braking force, or during a change in direction, are serious and involve a partial or even complete loss of control of the vehicle. It is therefore of paramount importance when travelling on a wet road to be able to anticipate the conditions for hydroplaning and better still to quantify such conditions.
To the driver of the vehicle, no warning sign, apart from seeing a wet road, precedes the onset of partial or complete hydroplaning—the danger cannot therefore be foreseen.
In addition, a measurement of hydroplaning provides information that proves essential for the various electronic assistance devices used, for example, for controlling an antilock braking system (ABS) of a vehicle, antiskid regulation (ASR) of driving wheels, trajectory control (ESP) or other forms of control or monitoring, such as for example for monitoring tire pressure. This is because such information, coupled for example with a measurement of grip (μ), would enable the effectiveness of the abovementioned devices to be greatly improved in real time.
Thus, at the moment that the start of hydroplaning is detected, not only can a warning be indicated to the driver of the vehicle, but also a measurement corresponding to an intensity or degree of this hydroplaning can be sent to the various active safety devices mentioned above, so as to modify or refine their triggering parameters.
It is known from U.S. Pat. No. 5,502,433 to detect hydroplaning, but this patent in no way teaches a method or a device for quantifying it, the patent merely describes the determination of a preset warning threshold that does not at all take into account a height of water liable to be present on the ground at the moment of hydroplaning. The water height parameter considerably modifies, at constant speed, both the moment of onset of hydroplaning and its intensity. The prior determination, as provided by the patent cited above, of a level of a threshold above which hydroplaning is assumed to be initiated therefore does not optimize an opportunity or even a reliability of a triggered warning.